21458309 has 2 divisors, whose sum is σ = 21458310. Its totient is φ = 21458308.

The previous prime is 21458303. The next prime is 21458321. The reversal of 21458309 is 90385412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15382084 + 6076225 = 3922^2 + 2465^2 .

It is a cyclic number.

It is not a de Polignac number, because 21458309 - 2¹⁶ = 21392773 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21458303) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10729154 + 10729155.

It is an arithmetic number, because the mean of its divisors is an integer number (10729155).

Almost surely, 2^21458309 is an apocalyptic number.

It is an amenable number.

21458309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21458309 is an equidigital number, since it uses as much as digits as its factorization.

21458309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8640, while the sum is 32.

The square root of 21458309 is about 4632.3114100846. The cubic root of 21458309 is about 277.8850386422.

The spelling of 21458309 in words is "twenty-one million, four hundred fifty-eight thousand, three hundred nine".